Method and system for assisting navigation using rendered terrain imagery

ABSTRACT

A digital computer system for displaying a computer generated terrain representing a 3-dimensional depiction of the real world terrain surrounding a vehicle in real-time while the vehicle is in motion. This 3-D (3-Dimensional) image is rendered in real time while the vehicle is in motion and uses Global Positioning System (GPS) or differential GPS (dGPS) data available from a GPS unit and translates that data into virtual space within an Image Generation Processing block of the digital computer system. The digital computer system generates a virtual world 3-D image representing the eye-point position of the vehicle and directional vector into a terrain database. Using the latitude, longitude, and altitude supplied from the GPS unit as the eye point position into a virtual world using a terrain database, the Image Generation Processing block has a render engine capable of rendering a depiction of the terrain outside of the vehicle, as would be seen in high visibility conditions, regardless of weather, lighting and atmospheric conditions.

FIELD OF THE INVENTION

The present invention relates generally to information display systemsand more specifically to a digital system for generating a 3-Dimensional(3-D) representation of real-world terrain which closely approximatesthe view seen when actually looking at the real-world terrain.

BACKGROUND OF THE INVENTION

In the navigation of a vehicle over a prescribed route contour maps arecommonly used to provide an indication of the terrain over which thevehicle is traveling. The information afforded by contour maps, assortedvehicle instrumentation, and visual observation enables the operator tonavigate the vehicle as it travels along its prescribed route. Thus, apilot navigating an aircraft, for instance, uses contour maps,instrumentation readings and visual observation in order to determinealtitude and other course parameters have traditionally defined anavigational instrument used primarily to aid in the navigation of thevehicle along a pre-defined path.

U.S. Pat. No. 4,682,160 issued to Beckwith Jr. et al. on Jul. 21, 1987,describes a system which generates a real time perspective view of theterrain lying along an aircraft's flight path for the benefit of thepilot of an aircraft employing the system. The system of the Beckwith,Jr. et al. patent accesses terrain data stored as digital information ina digital map generator and then converts the digital data into theperspective representation of the terrain which may be viewed on anappropriate input/output device, such as a cockpit CRT (cathode raytube) instrument panel. The real time perspective representationprovided to the pilot of the aircraft approximates the view the pilotwould have if actually looking out a window of the aircraft during highvisibility conditions.

The Beckwith et al. patent defines a hardware device that accessesterrain data which is converted into a perspective representation of theterrain which is displayed on a display device, such as a CRT instrumentpanel, for the pilot to see. The contour representation of the terrainon the display device represents a perspective as if the pilot wereactually viewing the terrain himself during high visibility conditions.The Beckwith et al. patent offers the advantage of allowing a pilot tofly during inclement weather conditions with the aid of a display whichprovides terrain information of the type that would be available to thepilot's naked eye during high visibility weather conditions.

The hardware implementation of the Beckwith et al. patent produces awire-frame model of the terrain over which the aircraft is flying. TheBeckwith et al. patent requires a great number of contour paths in orderto generate a wire-frame model of the terrain is a limitation.Additionally, the hardware approach of the Beckwith et al. patent doesnot provide as flexible a solution as could be achieved with a softwareapproach.

U.S. Pat. No. 5,488,563 issued to Chazelle et al. on Jan. 30, 1996defines a device that correlates the terrain data with the flight pathof an aircraft to define an anti-collision mechanism and warning system.Memory of the device stores terrain information of a very large area ofthe earth. As a function of the position of the aircraft, theappropriate local map is temporarily transferred into a fast accessmemory of the device and an altitude envelope of the aircraft isdeveloped given local terrain information, velocity and accelerationvectors for the zone in which the aircraft is flying. The device furtherhas anti-collision processing capabilities such that an alarm indicatesif the flight path of the aircraft violates a predetermined relationbetween a protection field and the altitude envelope. The Chazelle etal. patent uses either an inertial navigational unit or a radionavigational instrument to generate a synthetic image representative ofa flight path trajectory that will avoid collision with the terrain overwhich the airplane is flying. The synthetic image representative of aflight path trajectory is not a 3-D image of the terrain over which theairplane is flying.

The flight management technology of the Chazelle et al. patent studiesterrain curves in order to calculate an exit path for the airplane. Thepositional information required in order to calculate the exit pathnecessarily includes flight information parameters that must be suppliedby the flight management system of the aircraft. This is clearly shownby Informations in flight block 2 of FIG. 2 of the Chazelle et al.patent. Such flight parameters would include information with regard tothe inertial unit 20, radio navigational instrument 21, andRadio-altimeter 22 all shown in FIG. 3. The inertial unit 20 providesinformation on the velocity and acceleration of the aircraft from whichthe angle of incidence, yaw, slope, pitch, heading, and bank may bedetermined. The angular values are used in the vicinity of theacceptable flight deck of the aircraft.

There is currently an unmet need in the art to be able to provide anavigator of a vehicle with terrain information over which the vehicleis traveling regardless of weather and visibility conditions in a mannerthat is not dependent upon trip information such as velocity andacceleration of the vehicle and in a manner that is more flexible thanthe hardware solution to be found in the prior art. There is a need inthe art for the terrain information to be a 3-D, non-wire frame imagedifferent from the synthetic image representative of an exit pathgenerated by the invention of the Chazelle et al. patent. Additionally,there is an unmet need in the art to provide such terrain information tonavigators of a variety of vehicle types including, but not limited to,aircraft.

SUMMARY OF THE INVENTION

It is an object of the invention to be able to provide a navigator of avehicle with terrain information over which the vehicle is travelingregardless of weather and visibility conditions in a manner that is notdependent upon trip information such as velocity and acceleration of thevehicle and in a manner that is more flexible than the hardware solutionto be found in the prior art.

It is further an object of the invention to provide such terraininformation to navigators of a variety of vehicle types, including butnot limited to aircraft.

Therefore, in accordance with the present invention, a digital computersystem for displaying a computer generated terrain representing a3-dimensional depiction of the real world terrain surrounding a vehiclein real-time while the vehicle is in motion. This 3-D (3-Dimensional)image is rendered in real time while the vehicle is in motion and usesGlobal Positioning System (GPS) or differential GPS (dGPS) dataavailable from a GPS unit and translates that data into virtual spacewithin an Image Generation Processing block of the digital computersystem. The digital computer system generates a virtual world 3-D imagerepresenting the eye-point position of the vehicle and directionalvector into a terrain database. Using the latitude, longitude, andaltitude supplied from the GPS unit as the eye point position into avirtual world using a terrain database, the device can render adepiction of the terrain outside of the vehicle, as would be seen inhigh visibility conditions, regardless of weather, lighting andatmospheric conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the claims. The invention itself, however, as well as apreferred mode of use, and further objects and advantages thereof, willbest be understood by reference to the following detailed description ofan illustrative embodiment when read in conjunction with theaccompanying drawing(s), wherein:

FIG. 1 is a block diagram of the digital computer system, according tothe present invention;

FIG. 2 is an illustration of the controlled and restricted zones for aparticular space through which the vehicle is traveling;

FIG. 3 illustrates the lighting angle condition used by the presentinvention,

FIG. 4A illustrates the vertical field of view, according to the presentinvention.

FIG. 4B illustrates the horizontal field of view, according to thepresent invention.

FIG. 5 illustrates the "safe-distance" bubble parameter that causes theaudible and/or visual indicator to enunciate, according to the presentinvention; and

FIG. 6 illustrates the polygons set for 3 position points which definethe 3-D virtual image, according to an embodiment of the presentinvention.

DESCRIPTION OF THE INVENTION

The present invention is a digital computer system that correlatespositional input data, such as Global Positioning Satellite (GPS) ordifferental GPS (dGPS) data, into virtual space within a computer systemto generate the eye-point position of the vehicle into a simulated"real-world" image. A virtual reality image, which may be shaded ortextured if so desired, is generated at a real-time rate which depictsthe real-world terrain in front of the vehicle following the directionalvector of travel in front of the vehicle. The computer-generated imageis a view of 3-D space representing what would be viewed by the operatorof the vehicle during ideal weather conditions and may be a filledpolygonal image or a fractal image. The image generated by the digitalcomputer system is viewed on an instrument panel of a vehicle which hasaccess to the system. Thus the computer-generated image allows theoperator to view the terrain in the vehicle's directional vector oftravel in spite of restricted visibility conditions such as might becaused by smoke, ice, snow, rain, blizzards, nighttime.

The digital computer system of the present invention encompasses asoftware system that operates on a digital computer system. The digitalcomputer system has three major components required to generate thereal-time 3-D image: a database of terrain information, a 3-D renderengine, and a display device for displaying the 3-D image rendered bythe 3-D render engine. Reference to block diagram of the digitalcomputer system 10 of FIG. 1 illustrates the informational flow betweenthe three major components of the digital computer system 10 of thepresent invention: Terrain Database block 18, the render enginerepresented by Image Generation Processing block 24, and Display block26 through which the operator may view the rendered image generated byImage Generation Processing block 24. The Display block 26 represents aDisplay device which displays for the operator the real world terrainsurrounding the vehicle. The computer generated scene is a view of the3-D space representing what would be viewed of the real world if viewedby the operator of the vehicle during ideal weather and lightingconditions.

Position Information block 14 of the digital computer system 10 containsGPS (Global Positioning Satellite) data or dGPS (differential GlobalPositioning Satellite) data received from GPS unit 12, hereinafterreferred to as GPS data. The GPS system allows civilians access totwenty-four satellites in orbit around the earth. The GPS system takesdirectional information from each of three or four of the twenty-foursatellites, using a 3-D triangulation measurement, in order to compute aposition. It is important to note that the FM (Federal AviationAdministration), on Dec. 7, 1995, approved the use of differential GPSfor instrument approaches to otherwise restricted airports. This isexpected to greatly expand the number of IFR rated airports in theUnited States in the future.

GPS unit 12 is representative of a variety of GPS systems which usestandard interface protocols, such as the National Marine EquipmentAssociation 0183 or Trimble Standard Interface Protocol. The digitalcomputer system 10 translates the GPS or dGPS data into virtual spacewithin the Image Generation Processing block 24 of digital computersystem 10. Image Generation Processing block 24 may be any imageprocessing technology, including image processing technologycommercially available.

In addition to the GPS data, Image Generation Processing block 24 isprovided with information from the Terrain Acquisition block 20 in orderto generate a computer image of the terrain over which the vehicle istraveling that may be viewed at Display block 26. Given the GPS data andterrain data, Image Generation Processing block 24 uses a render engineto generate the 3-D image. A render engine may be defined as code thatwill generate an image based upon terrain database information andeyepoint position. The computer image produced by Image GenerationProcessing block 24 and viewed at Display block 26 represents theeye-point position and directional vector of the vehicle in thesimulated "real-world" image of the vehicle into the terrain database.The Display device represented by Display lock 26 may be any number ofappropriate devices known in the art. For instance, the Display devicemay employ a CPU (central processing unit) with an embedded operatingsystem (O/S) and code; naturally, such a Display device with embeddedcode must have enough RAM (random access memory) in order to execute thecode. The Display device may be a storage device such as a CD ROM(compact disk read only memory) which stores data for the terraindatabase over which the vehicle is traveling for that given trip. The3-D image itself may be displayed upon any display device such as anactive matrix LCD (liquid crystal display) screen that is located on theinstrument panel of the vehicle.

As previously discussed, the positional information of PositionInformation block 14 of the vehicle is acquired from a GPS system,represented by GPS Unit 12, and is used to determine the eye pointposition in a database of real-world terrain data. The GPS system takesdirectional information from each of three or four satellites to computea position, using the 3-D triangulation method. GPS data or dGPS dataprovides information concerning Latitude Degrees & Minutes, LongitudeDegrees & Minutes, Altitude in meters above the average/mean sea level,and Time to digital computer system 10; Velocity information may or maynot be available on all GPS systems. The Latitude, Longitude, Altitude,and Time values may be used to define a position in 3-Dimensional spacewhich is mapped to a corresponding location in a virtual reality worldwhich will exactly mimic the real-world which actually exists outsidethe vehicle.

Information related to the Latitude, Longitude, Altitude, Time andVelocity of the vehicle, allows a 4-point spatial location, representedby (X, Y, Z, T), to be derived by Location Calculations block 16 giventhe GPS data, where X is representative of Latitude in degrees andminutes, Y is representative of Longitude in degrees and minutes, Z isrepresentative of Altitude in meters, and T is representative of time.Typically, T is representative of time at a resolution of 0.5 second.The 4-point spatial location is useful in determining a number of usefulparameters related to the trip of the vehicle. These parameters to bedetermined using the 4-point spatial relationship include the positionof the vehicle in relation to the real-world database coordinates usingeither longitude/latitude or Universal Transverse Mercator units; thedirectional vector of travel using the last set of coordinates includingheading and pitch; and the velocity, v=d/t, at which the vehicle istraveling.

The GPS data must be sampled periodically at short enough intervals torender a reliable image of the vehicle in the terrain it istransversing. Thus, Position Information block 14 of the digitalcomputer system 10 samples GPS positional data at least every 1/2 secondif possible or even faster if possible; if 1/2 second output from theGPS system is unavailable, the digital computer system 10 retrieves GPSdata as rapidly as it is available. The faster the sampling, the morerealistic the real-time image produced by Image Generation Processingblock 24 will be. It will be understood by one of ordinary skill in theart, therefore, that sampling may occur so frequently as to becharacterized as "continuous sampling" where positional input data iscontinuously received by Position Information block 14. The ImageGeneration Processing block 24 of digital computer system 10 then drawsa smooth "animation" of the movement of the vehicle based upon the lastknown position and the speed of the vehicle.

Using the latitude, longitude, altitude, and direction of travel as theeye point position for a terrain database, the digital computer systemcan render a depiction of the terrain along the directional vector ofthe vehicle by referencing the last positional reading in order tocompute the heading and pitch of the current position of the vehicle. Itshould be noted that location A is the next to last positional readingat time T1 while location B is the last positional reading of thevehicle at time T2. By appropriately manipulating the latitude,longitude, and altitude readings of two subsequent readings at time T1and time T2, it is possible to generate a directional vector and tocalculate the velocity of the vehicle.

Computing the heading and pitch of the current position of the vehicleis accomplished though simple geometry through the use of a lookuptable, an example of which is included here for completeness:

For locations, A=(X₁, Y₁, Z₁, T₁) and B=(X₂, Y₂, Z₂, T₂)

Heading: sin() lookup of: ##EQU1## Pitch: sin()look up of: ##EQU2##Pitch is correlated against 90° increments for relative attitudecorrectness.

The vector AB defines the directional vector, and the velocity of thevehicle is obtained by: ##EQU3## It should be noted that differentialGPS (dGPS) data provides more accurate positional information than doesGPS data. DGPS data is the result of coupling GPS data with correctionalinformation to reduce the error inherent in the GPS system. A radiosignal from a ground-based system is used to "correct" the error foundin GPS data. While conventional GPS data has an accuracy ofapproximately 100 meters, dGPS has a much greater accuracy ofapproximately 1 to 10 meters. Either GPS data or dGPS data may be usedin the present invention.

The digital computer system 10 correlates the eyepoint position aoperator of the vehicle would have with a terrain database locationprovided by a GPS system in order to generate the virtual image of thereal-world terrain following the directional vector of travel in frontof the vehicle. This correlation can be accomplished different ways.Pure longitude/latitude data may be used or longitude/latitude data maybe converted to Universal Transverse Mercator units or any similarpositional locus units.

The terrain database 18 derived from a GPS system as previouslymentioned is preferably based on the highest possible resolution terraindata available from sources such as the United States GeologicalSociety, the Department of Defense, and/or the Defense Mapping Agency.The data of terrain database 18 is typically provided at 30 meterspacing and is used by Image Generation Processing block 24 to generatethe 3-D image seen on Display block 26. The terrain data included interrain database 18 is a subset of the data contained in PositionalInformation block 14 which is received from GPS Unit block 12.Nonetheless, the number of data points represented by terrain database18 is quite staggering. Assuming that terrain database 18 is a sectionalchart having a size of 600 NM (nautical miles)×400 NM with a resolutionof 30 meter spacing, a total of 914,628,720 data points are represented!Obviously this represents too many data points to fit onto a single CDand additionally would require quite a bit of access time upon power-upof the digital computer system.

The terrain data contained within Terrain Database 18 is used topre-generate terrain database 18 of the real-world terrain of theapplicable travel plan and is put onto a storage device, such as aCD-ROM, that is made available to the digital computer system 10 uponpower-up. Upon power-up of the digital computer system 10, the system 10reads the GPS position, including directional vector information, andgenerates a 3-D scene depicting the forward view of the vehicle in theterrain.

Terrain Database 18, in addition to containing GPS terrain information,might also contain sectional chart information about objects such aswires, frequencies, restricted airspace, control zones, landmarks suchas towers etc. This sectional chart information is integrated into theterrain database such that can be displayed to the operator uponrequest. The sectional chart information is used to addtransparent/translucent cylinders or objects of "color" aroundcontrolled zones and/or restricted zones for the sectional area throughwhich the vehicle is currently traveling. Referring to FIG. 2, anillustration of the controlled and restricted zones for a particularterrain, such as airspace, through which the vehicle operator istraveling is shown.

In addition to the sectional chart information and terrain informationprovided by terrain Database 18, the digital computer system 10 may beprovided with additional information at Other Inputs block 22. Thus thedigital computer system 10 can also acquire radar input from either anon-board weather radar system or from an on-board TCAS (TrafficCollision Avoidance System) thereby having the ability to incorporateweather conditions or information concerning the location of othervehicles in the region into the generated 3-D image. Such additionalinformation provided by Other Inputs block 22 is incorporated with theterrain database and sectional chart information by Image GenerationProcessing block 24. As can be seen in FIG. 2, the informationconcerning sectional chart information, terrain information, and otherparameters is extremely valuable to air traffic control management.

The positional information derived by Location Calculations block 16from data received from Position Information block 14 is used inconjunction with the terrain database by Image Generation Processingblock 24 to create the 3-D image.

The 3-D image produced by Image Generation Processing block 24 and shownat Display block 26 is a depiction of the terrain in front of thevehicle with the light source at 12:00 "high-noon" and at infinity. Thisdefault lighting condition permits the Display block 26 to alwaysdisplay a scene relative to "ideal" conditions, regardless of the actualconditions which might exist outside the vehicle. The lighting anglecondition used by the present invention is illustrated in FIG. 3.

The field of view (FOV) contained in the 3-D image generated by ImageGeneration Processing block 24 is selectable within given parameters.The rendered FOV is selectable from 60° to 145°, horizontal HFOV (HFOV)and vertical FOV (VFOV). The FOV is selected with care since too large aFOV value may cause the scene to appear "fish-eyed" and therefore oflittle use; too small a FOV value may limit the amount of data displayedmaking the rendered image unusable. Selectable FOV allows the 3-D imageto be put on different sized screens for viewing by the operator.Examples of a 90° HFOV and a 90° VFOV are illustrated in FIGS. 4A and4B.

It should be noted that the distant terrain shown in the 3-D imagegenerated by Image Generation Processing block 24 is generated as afunction of the speed of the vehicle. Typically, the distant terrainrepresents the terrain a given number of seconds from the vehicle'spresent position along the vehicle's directional vector of travel. Thedistance parameter of the 3-D image is calculated in real-time so as toallow the digital software system 10 to be used with all types ofvehicles, including both air and ground vehicles.

The 3-D image generated by Image Generation Processing block 24 is arepresentation of the terrain that may be based upon polygonal orfractal image technology. A fractal repesentation is based upon discretepoints and thus generally has a higher resolution image than a filled3-D polygonal image. For a polygonal filled 3-D image, a fairly simplecalculation on each polygon in the rendered scene can result in adistance coefficient from the vehicle to the intersection of the planeof the polygon. The render engine of Image Generation Processing block24, as previously discussed, is code that will generate the 3-D imagebased upon both terrain data and eyepoint position. In the case of apolygonal filled 3-D image, the render engine is able to translate thepolygon list into the 3-D image.

From the rate of travel of the vehicle, it can then be determined if thepolygon lies within another configurable parameter, the "safe-distance"bubble of the vehicle. The "safe-distance" bubble parameter is set bythe operator of the vehicle and allows the digital computer system 10 tobe easily used in conjunction with vehicles of different sizes, such aswith a smaller, slower vehicles or faster, larger vehicles. After thesize of the "safe-distance" bubble parameter has been set by theoperator, should a polygon within the 3-D image come within the"safe-distance" bubble of the vehicle, an audible and/or visualindicator such as an alarm will inform the operator. The bubbleintersection caused by a polygon invading the safe area established bythe "safe-distance" bubble parameter that causes the audible and/orvisual indicator to enunciate is shown in FIG. 5.

In the 3-D image presented to the operator of the vehicle, the polygonsof that image have color, texture and other indicators which indicatewhat type of surface is being represented. For instance, Dark Blue maybe representative of water, Green-Land representative of Sky-Blue, Grayrepresentative of Buildings or other protruding land masses, and Whiterepresentative of surfaces above the "tree-line". Since the databaseshall be generated prior to "run-time" and shall be stored on a storagedevice, such as a CD-ROM or other storage device, the color, texture,and other indicators conveyed by the polygon is pre-determined and usedby the 3-Dimensional render engine provided by Image GenerationProcessing 24 at run-time. Coloring the polygons allows for a "baseline"color before any shading has occurred. Subsequent shading providesmotion queuing to the operator of the vehicle as the vehicle traversesthrough the database.

The polygons of the 3-D image are defined by taking 3 position pointsfrom the terrain database 18 in order to generate a flat surface for therender engine represented by Image Generation Processing 24 at thatpoint in the 3-D image. By using multiples of these triplets of terraindata, an fairly accurate rendition of the surface can be developed bythe Image Generation Processing 24. The definition of the polygons ofthe 3-D image by 3 position points is illustrated by FIG. 6.

The digital computer system 10 can optionally display a "cross-hair" inthe center to of the display which depicts the projected flight path ofthe vehicle. Should this cross-hair intersect with a rendered polygoninside the safety bubble, a visual and/or audible alert will eitherflash or sound requiring the operator to acknowledge this intersection.The device allows the operator to select either a cockpit view or atrailing view, which depicts a view of the vehicle in the 3-D scene asseen from behind the vehicle. Obviously, the 3-D image produced byDisplay block 26 should be within easy viewing distance of the operatorin the vehicle.

The operator of the vehicle uses the digital computer system of thepresent invention when nighttime or other restricted visibilityconditions precipitate the need for the operator to be able to "see" theterrain over which the vehicle is traveling in spite of the restrictedvisibility conditions. The present invention is not intended to be usedas the sole navigational device in inclement weather or lightingconditions, but rather serves as a supplemental device to assistconventional IFR navigational devices. The operator of the vehicle is touse the present invention when questions of location, or outsideconditions warrant the use of the device to "see" into otherwise blindconditions. Because operation of the digital computer system isindependent all other navigational instruments, save for the GPS systemon-board the vehicle, the digital computer system is capable as servingas a secondary back-up device for all other navigational instrumentson-board the vehicle.

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A digital computer system that correlatespositional input data for generating a 3-D virtual image,representational of a localized terrain over which a vehicle istraveling, comprising:a positional information unit which receives thepositional input data provided by a satellite-based positioning system;a terrain database unit, containing data of the localized terrain overwhich the vehicle is traveling; and a location calculation unit whichreceives the positional input data from the positional information unitand generates a most recent spatial location of the vehicle in thelocalized terrain over which the vehicle is traveling; an imagegeneration processing unit having a render engine which receives datafrom the positional information unit and the terrain database unit andwhich generates the 3-D virtual image representational of the terrainover which the vehicle is traveling, wherein the image generationprocessing unit generates the 3-D virtual image by referencing the mostrecent spatial location of the vehicle in the localized terrain overwhich the vehicle is traveling in order to compute a heading, a pitch,and a directional vector of a current position of the vehicle, whereinthe most recent spatial location of the vehicle is generated by thelocation calculation unit.
 2. The system of claim 1, wherein the headingand the pitch of the current position of the vehicle are computedthrough the use of a lookup table.
 3. The system of claim 1, wherein thesystem further comprises:a radar information unit that provides radardata to the image generation processing unit, wherein the imagegeneration processing unit incorporates the radar data from the radarinformation unit with data from the terrain database unit and thepositional information unit to generate the 3-D virtual imagerepresentative of the terrain over which the vehicle is traveling. 4.The system of claim 3, wherein the radar information unit is a weatherradar system and the radar data is representative of weather conditions.5. The system of claim 3, wherein the radar information unit is atraffic collision avoidance system (TCAS) and the radar data isrepresentative of vehicular traffic.
 6. A digital computer system thatcorrelates positional input data for generating a 3-D virtual image,representational of a localized terrain over which a vehicle istraveling, comprising:a positional information unit which receives thepositional input data provided by a satellite-based positioning system;a terrain database unit, containing data of the localized terrain overwhich the vehicle is traveling; and an image generation processing unithaving a render engine which receives data from the positionalinformation unit and the terrain database unit and which generates the3-D virtual image representational of the terrain over which the vehicleis traveling, wherein the image generation processing unit generates the3-D virtual image by referencing a most recent spatial location of thevehicle in the localized terrain over which the vehicle is traveling inorder to compute a heading and a pitch of a current position of thevehicle, wherein the most recent spatial location of the vehicle isgenerated by a location calculation unit which receives the positionalinput data from the positional information unit.
 7. The system of claim6, wherein the heading and the pitch of the current position of thevehicle are computed through the use of a lookup table.
 8. The system ofclaim 6, wherein the system further comprises:a radar information unitthat provides radar data to the image generation processing unit,wherein the image generation processing unit incorporates the radar datafrom the radar information unit with data from the terrain database unitand the positional information unit to generate the 3-D virtual imagerepresentative of the terrain over which the vehicle is traveling. 9.The system of claim 8, wherein the radar information unit is a weatherradar system and the radar data is representative of weather conditions.10. The system of claim 8, wherein the radar information unit is atraffic collision avoidance system (TCAS) and the radar data isrepresentative of vehicular traffic.
 11. method for generating a 3-Dvirtual image representational of a localized terrain over which avehicle is traveling, comprising the steps of:receiving positional inputdata provided by a satellite-based positioning system which provideslatitude data, longitude data, altitude data, and time data to define aspatial location representative of an eye point position seen by anoperator of the vehicle in the terrain over which the vehicle istraveling; deriving an initial positional reading of the vehicle at timeT1 from a sampled GPS data, wherein the initial positional reading attime T1 is represented as A =(X₁, Y₁, Z₁, T₁) where X₁ is representativeof latitude at time T₁, Y₁ is representative of longitude at time T₁,and Z₁ is representative of altitude at time T_(1;) deriving asubsequent positional reading of the vehicle at time T2 from the sampledGPS data, wherein the subsequent positional reading at time T2 isrepresented as B=(X₂, Y₂, Z₂, T₂) where X₂ is representative of latitudeat time T2, Y₂ is representative of longitude at time T2, and Z₂ isrepresentative of altitude at time T₂ ; calculating a directional vectorof the vehicle defined as the vector AB; calculating the velocity of thevehicle according to the equation: ##EQU4## generating a computer imagerepresentative of the eye point position seen by the operator of thevehicle and the directional vector of the vehicle, wherein the computerimage is generated by a render engine of an image generation processingunit; and overlaying the computer image representing the eye pointposition and the directional vector of the vehicle onto a simulatedimage of the terrain over which the vehicle is traveling to generate a3-D virtual image.
 12. The method of claim 11, comprising the furtherstep of:displaying the 3-D virtual image.
 13. The method of claim 11,wherein the sampled global positioning satellite (GPS) data isdifferential global positioning satellite data.
 14. The method of claim11, wherein the step of overlaying the computer image representing theeye point position and the directional vector of the vehicle onto thesimulated image to generate the 3-D virtual image is accomplished by animage generation processing block of a digital computer system.
 15. Themethod of claim 11, wherein the step of receiving positional input datais accomplished by periodically sampling global positioning satellite(GPS) data.
 16. The method of claim 15, wherein the GPS data ispreferably sampled as often as possible.
 17. The method of claim 16,wherein the GPS data is sampled at least every 1/2 second.
 18. A digitalcomputer system that correlates differential positional input data forgenerating a 3-D virtual image, representational of a localized terrainover which a vehicle is traveling, comprising:a positional informationunit which receives the differential positional input data provided by asatellite-based positioning system, wherein the differential positionalinput data is a differential GPS data provided from a Global PositioningSatellite (GPS) unit; a terrain database unit, containing data of thelocalized terrain over which the vehicle is traveling; an imagegeneration processing unit having a render engine which receivesdifferential data from the positional information unit and the terraindatabase unit and which generates the 3-D virtual image representationalof the terrain over which the vehicle is traveling; and a radarinformation unit that provides radar data to the image generationprocessing unit, wherein the image generation processing unitincorporates the radar data from the radar information unit with datafrom the terrain database unit and the positional information unit togenerate the 3-D virtual image representative of the terrain over whichthe vehicle is traveling.
 19. The system of claim 18, wherein the radarinformation unit is a weather radar system and the radar data isrepresentative of weather conditions.
 20. The system of claim 18,wherein the radar information unit is a traffic collision avoidancesystem (TCAS) and the radar data is representative of vehicular traffic.